| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 107 === Lab-on-chip has been a popular research topic in recent years. The latest actuator is driving droplets on interdigitated electrodes using the mechanism so called “dielectrowetting”. This kind of device only require a single plate of electrodes.
This system does not require the top plate (cover), allowing for the handling of a much wider range of liquid volumes with easily accessible and simplified structures. Bus so far, we don’t fully understand the dynamics behavior of droplets during actuating process. This paper is focus on the dynamics behavior of droplets in digital microfluidic actuator driven by dielectrowetting.
In this experiment, we represented a dielectrowetting device with super-hydrophobic treatment and placed a drop of DI water (30μl) on its surface. We measured the advancing angle, receding angle, contact angle hysteresis and critical sliding angle of droplet under stationary condition. By applying an external electric field (AC), we observed how the magnitude of voltage influences the contact angle and the reaction time for droplet to get to new equilibrium state.
After that, we let droplets roll freely down on the surface of dielectrowetting device which was inclined at a certain angle. Its path was deflected due to the dielectrowetting effect created by electrodes which placed on the surface with 45 degree of included angle. We measured the lateral displacement of droplet and it has positive correlation with magnitude of voltage. Results also showed that the force which caused droplet to deflect mainly happened on the edge of electrode and it can’t be contributed to difference of contact angle between two surfaces.
Hence, we redesigned the alignment of electrodes, now with parallel and vertical to the path of droplet. The behaviors of droplet were significantly different when passing through two kind of electrode that mentioned above. Proofing that the phenomenon of directional wettability in dielectrowetting has huge impact on dynamics of droplet.
In order to obtain more accurate data on dynamics contact angle, we fixed the droplet on a hydrophilic upper surface. By moving the electrodes on lower plate with constant velocity, we have measured the dynamics contact angle under different applied voltage. Finally, we used molecular kinetic theory to analyze dynamics contact angle. We discovered that our model is suitable to describe the dynamics angle change due to the influence of dielectrowetting, but only comply when applied electric field is parallel to the path of droplet. Further research is needed when applied electric field is vertial to the path of droplet.
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